Most compressor cooling systems used in today's household refrigerators use a capillary tube to reduce the pressure of the refrigerant flowing from condenser to evaporator. Further, many of these cooling systems do not run continuously, but turn on and off in cycles. There is then a compressor on-phase followed by a compressor off-phase. In these systems there are typically two kinds of efficiency losses.                Efficiency losses related to refrigerant vapor that flow from condenser to evaporator, through the capillary tube during the compressor off-phase. Since nothing stops the vapor from flowing through the capillary tube during compressor off time, this will happen until the pressures are equalized.        Efficiency losses related to that the evaporator and condenser pressures vary during the compressor on-phase. The refrigerant mass flow rate through the capillary tube is a function of evaporator and condenser pressure. When the pressure difference between evaporator and condenser is high the flow rate is high, and vice versa. This means, unfortunately, that the mass flow rate through the capillary tube does not always correspond to the flow rate that would be optimum for the system. At the start of the compressor on-phase, the pressure difference is lower than at the end of the compressor on phase. This means that the refrigerant flow rate through the capillary tube is lower at the start than at the end of the compressor on-phase. Unfortunately, the flow rate through the capillary tube that would be optimum for the system, vary in the opposite way. In other words, it would typically be better with a higher flow rate at the start than at the end of the compressor on-phase.        
To decrease losses resulting from migration of refrigerant during compressor off-phase, an open/close valve can be installed in series with the capillary tube, to stop the refrigerant flow through capillary tube during the time that the compressor is in the off-phase, i.e. when the compressor is not running. In such a system a refrigeration system may use an open/close valve located on the path from the condenser to the evaporator to prevent refrigerant migration from the condenser to the evaporator of the refrigeration system during a compressor off-phase. The valve is set to a closed state during the compressor off-phase and set to an open state during the compressor on-phase. Hereby energy loss resulting from refrigerant migration can be eliminated or at least reduced.
A refrigeration/freezer system as described above is depicted in FIG. 1. Further, in some refrigeration systems, the use of a valve that is in a closed state during a compressor off period results in that the compressor will have to start against a pressure difference between the condenser and evaporator. In order to reduce the need for an increased start torque the valve can be opened a predetermined period before the start of the compressor. This can equalize the pressure difference and may thereby reduce the required start torque. Such a refrigeration system is described in the U.S. Pat. No. 8,161,763.
There is a constant desire to improve the performance in a refrigerant system and to provide more efficient refrigeration system. Hence, there is a need for an improved refrigerator apparatus and to a cooling system used in a refrigerator.